Spinal cord injury is thought to result in rapid & severe osteoporosis & is considered to be a common cause of disuse atrophy of bone. This condition predisposes the spinal cord injured pt to the risk of fracture & disability. The evolution & natural course of bone resorption following SCI, however is poorly understood & has not been well described. A biochemical assay for urinary cross-linked N-telopeptides of type I collagen has recently been developed & has been shown to be a specific marker for bone resorption activity. To our knowledge, this assay has not been previously applied to the SCI population. In this pilot study, the NTx assay will be used, in a prospective manner, to characterize the biochemical profile of bone resorption in a group of acute (group 1, n=10) and chronic (group 2, n=10, >6 mos post-injury) post-traumatic SCI patients. These two groups will each be compared with yoked controls, consisting of individual groups of age-matched uninjured subjects (group 3, n=20 and group 4, n=20). Analysis of variance will be used to identify any significant differences in NTx activity between groups and within each group over time. The goals of the study are to measure the NTx activity in normal controls and in patients with acute and chronic SCI over time in order to develop a clinically useful system to monitor the progression of osteoporosis following SCI. For the period 12/1/95-11/30/96, 2 chronic group SCI patients were enrolled in the study and a single urine specimen was obtained. Recruitment of acute SCI patients is anticipated to begin during the winter months. Samples are stored in a GCRC core laboratory freezer prior to analysis. Biochemical assays will be performed once several specimens have been collected.